From experimental data available for pure rare‐earth iron garnets (RIG) an empirical method of estimating Faraday rotation (FR) in some mixed rare‐earth iron garnets is proposed. First, the Fe3+contribution to FR is extracted from YIG. From this value and from FR data available for several RIG, one is able to separate the contribution from different RE ions. Finally, FR in mixed rare‐earth iron garnets is calculated using simple scaling and results compared with data available in the literature. The agreement obtained is quite encouraging.